It is proposed to study the adenosine receptor which is coupled to adenylate cyclase, mainly in turkey erythrocytes and in the rat central nervous system. Attempts will be made to synthesize a radioactively labeled probe for the adenosine receptor, such that the direct monitoring of adenosine receptors will become feasible. Attempts will also be made to synthesize labels for the adenosine receptor. One such compound has already been prepared. Affinity labels are extremely important for the study of the mode of coupling between the adenosine receptor and adenylate cycylase. The mode of coupling of the adenosine receptor with adenylate cyclase will be studied in detail using a variety of experimental approaches. A radioactively labeled irreversible probe for the adenosine receptor will also be useful to characterize the subunit(s) of the adenosine receptor. Fluorescent adenosine analogues and fluorescent xanthine analogues will be prepared to monitor the detailed histochemical distribution of adenosine receptors in vivo. In parallel, attempts will be made to solubilize the adenosine receptor and to purify it, if we succeed to develop an assay for the adenosine receptor in the solubilized state.